It is very disappointing that this lesson does not appear to have been modified to deal with the poor distinction over when to use le/la/l'/le with ne. ni. ni. The lesson clearly states "When using ni, you omit the article after ni, unless you're talking about general things and using le, la, l', les."
Yet much of the discussion here has suggested the article should be used for the specific rather than the general. Better and more examples of when and how to use articles are needed - yet this has clearly been an issue for years.